This invention relates generally to color cathode ray picture tubes and is addressed particularly to an improved front assembly component for color tubes that have a tension foil shadow mask. The invention is applicable to tension mask tubes of various types including those intended for home entertainment television receivers and for medium-resolution and high-resolution tubes for color monitors.
A color cathode ray tube typically has three electron guns arranged in an in-line configuration. Each gun projects an electron beam through the apertures of a "shadow mask" onto assigned target areas located on the inner surface of the faceplate. The target areas comprise patterns of phosphor deposits typically arranged in triads of dots or lines. Each of the triads consists of a deposit of a red-light-emitting, green-light-emitting, and blue-light-emitting phosphor which are excited to luminescence under bombardment by the respective electron beams. To increase the apparent brightness of the display, and to minimize the incidence of color impurities that can result if a beam falls upon an unassigned phosphor deposit, the target area may include a layer of light-absorbing material termed a "grille" that surrounds each of the phosphor deposits.
The front assembly of a color cathode ray tube essentially comprises the faceplate with its deposits of the grille dag and the light-emitting phosphors, a shadow mask, and a support structure for the mask. As is well known in the art, the shadow mask is precisely spaced from the inner surface of the faceplate. The shadow mask acts as a color-selection electrode, or parallax barrier, that ensures that each of the three beams lands only on its assigned phosphor deposits.
This invention is concerned with a tension foil shadow mask that comprises an apertured metallic foil which may, by way of example, be about one mil or less in thickness. This type of mask must be supported in high tension a predetermined distance from the inner surface of the cathode ray tube faceplate--a distance known as the "Q-distance". The mask tension for a 14-inch tension mask cathode ray tube may be in the range of 20 to 40 kpsi, by way of example.
The physical requirements for the tension foil shadow mask support structure are stringent. As the shadow mask is mounted under high tension, the structure must be of high strength so that the mask is held immovable--an inward movement of the mask of as little as one-tenth of a mil can result in loss of guard band and consequent color impurities. Also, the mask support structure must be of such configuration and material composition as to be compatible with the means to which it is secured. For example, if the mask support structure is attached to glass such as the glass of the inner surface of the faceplate, it is essential that the material from which the structure is made have about the same thermal coefficient of expansion as that of the glass so the glass will not crack as a result of thermal stress. Also, the mask support structure must be of such composition that the mask can be securely fastened to it by means such as electrical resistance welding, by way of example. It is also preferable that the surface to which the mask is secured be of such flatness that no voids between the metal of the mask and the surface can exist to prevent the intimate metal-to-metal contact required for positive welding.
Prior art includes: Moore--U.S. Pat. No. 3,894,321; Strauss--U.S. Pat. No. 4,547,696; Palac--U.S. Pat. No. 4,100,451; Dougherty--U.S. Pat. No. 4,045,701; Steinberg et al--U.S. Pat. No. 3,727,087; Oess--U.S. Pat. No. 3,284,655; Hackett et al--U.S. Pat. No. 3,030,536; Vincent--U.S. Pat. No. 2,905,845; Fischer-Colbrie--U.S. Pat. No. 2,842,696; Law--U.S. Pat. No. 2,625,734; also, an article titled "The CBS Colortron: A color picture tube of advanced design." Fyler, et al. Proc. of the IRE, Jan. 1954; and a Tektronix, Incorporated specification sheet: "Avionics Color Cathode Ray Tube," TEK T8100; also a digest of a Tektronix journal article: "A High Brightness Shadow-Mask Color CRT for Cockpit Displays," Society for Information Display, Philadelphia. May 1983.